The present invention pertains to an improved controlled release potassium chloride tablet and a process for its preparation. More particularly, the present invention relates to a potassium chloride tablet prepared from microcapsules of potassium chloride crystals coated with two distinct layers, the first of ethylcellulose and the second of a hydrophilic polymer, preferably hydroxypropylcellulose. These microcapsules are capable of being compressed into tablets of suitable hardness and friability with minimum compression and quantities of excipients.
Sustained release formulations consisting of microencapsulated pharmaceutical agents coated with a single layer composed of ethylcellulose have been disclosed. Anderson, et al. disclose aspirin coated with a single layer of ethylcellulose (U.S. Pat. No. 3,341,416). Miller, et al. disclose a process for coating aspirin crystals with a single layer of polymeric material, such as ethylcellulose (U.S. Pat. No. 3,155,590). Tamas discloses a process for the preparation of sustained release solid pharmaceutical compositions which contain crystals of an active ingredient coated with a single layer of a polymer such as ethylcellulose (U.S. Pat. No. 4,748,023). Lippman, et al. disclose a controlled release capsule containing potassium salt coated with ethylcellulose and external surfactant having an HLB in excess of 10 (U.S. Pat. No. 4,259,315).
Other standard controlled release formulations consisting of microencapsulated pharmaceutical agents coated with a single layer of a polymer mixture have been disclosed. Bechgaard, et al. disclose a controlled release tablet or capsule with contains a core comprising an active agent and coated with a diffusion membrane which is insoluble in gastrointestinal fluids which may include ethylcellulose (U.S. Pat. No. 4,193,985). Samejima, et al. disclose the coating of microcrystals with a single layer consisting of a polymer mixture, such as ethylcellulose and hydroxymethylcellulose (U.S. Pat. No. 4,462,982). Pedersen, et al. disclose a controlled release composition containing a core of active agent which may be potassium chloride coated with a water insoluble, but water diffusible, layer consisting of a mixture of a solvent, a film-forming substance which may be ethylcellulose, and a hydrophobic substance (U.S. Pat. No. 4,572,833). Roswell, et al. disclose a controlled release composition containing a core of active agent which may be potassium chloride coated with a water insoluble, but water diffusible, layer consisting of a mixture of a solvent, a film-forming substance which may be ethylcellulose, and a hydrophobic substance with particles of the active agent adhered to the coating (U.S. Pat. No. 4,574,080). Hsiao discloses a sustained release dosage form of quinidine-coated pellets coated with a single layer which consists of a mixture of ethylcellulose and hydroxypropylcellulose (U.S. Pat. No. 4,634,587). Snipes discloses controlled release potassium chloride crystals coated with a single layer of a two component polymer mixture which consists of 85-97% ethylcellulose and 3-15% of an amphiphile (U.S. Pat. No. 4,832,955). Hsiao, et al. disclose a controlled release potassium chloride tablet form for oral administration which contains potassium chloride crystals coated with a single layer which consists of a mixture of ethylcellulose and either hydroxypropylcellulose or polyethylene glycol (U.S. Pat. No. 4,863,743).
Still other sustained release formulations consisting of microencapsulated pharmaceutical agents coated with a plurality of polymeric coatings have been disclosed. Zeitoun, et al. disclose compressed tablets for disintegration in the colon which contain a core of an active ingredient and a two-layer coating, the inner coating which may be of ethylcellulose controls the diffusion of the active ingredient and an enteric outer coating of an organic polymer (U.S. Pat. No. 4,432,966). Kjornaes, et al. disclose a sustained release tablet which contains crystals of the active ingredient coated with an inner layer of an aqueous dispersion of a film-forming agent which causes adhesion between the crystals at elevated temperatures and an outer layer of a water-based, film-forming agent which prevents adhesion of the crystals during heating, imparting flowability (U.S. Pat. No. 4,716,041).